The search for strong analgesics which also possess minimal potential for dependency has been among the highest priority efforts in pharmacological research. These research efforts have, to a great extent, involved chemical modifications of the opiate structure and the discovery of chemically novel compounds which possess morphine-like activity.
The discovery of endogenous polypeptide opioids has led workers in the field to consider that these peptides, possessing less rigid structures, might interact with opioid receptors other than those to which the classical rigid structure opiates, such as morphine, bind.
The concept of multiple opioid receptors has been supported by studies with nalorphine and a series of benzomorphans which display unusual pharmacological properties dissimilar from morphine, yet blocked by selective opioid antagonists. [See for example, W. R. Martin et al., J. Pharmacol. Exp. Ther., 197: 517-532 (1976)].
The existence of multiple types of opioid receptors is of importance because of the possibility of separating desirable analgesic and psychotherapeutic effects of a drug compound from the undesirable abuse potential or habituating effects.
U.S. Pat. No. 4,145,435 describes certain 2-amino-cycloaliphatic amide compounds as analgesics. In particular, trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzacetamide has been reported to possess selective kappa opioid receptor agonist activity, and therefore to possess analgesic activity without attendant dependence liability. [See P. V. Vanvoigtlander et al., J. Pharmacol. Exp. Ther., 224: 7-12 (1983)].
Recently the diuretic effect of various opioid agonists and antagonists has been studied, and it has been shown that kappa agonists tend to increase urination, while mu agonists decrease urination. [See J. D. Leander, J. Pharmacol. Exp. Ther., 227: 35-41 (1983)]. These findings indicate that selective opioid agonists and antagonists also possess potential as diuretics.